1. Field of the Invention
The present invention generally relates to methods and apparatuses used in vacuum processing systems of the type used to fabricate integrated circuits and flat panel displays. Specifically, the present invention relates to methods and apparatuses for cooling a rotating element in or about a process chamber of a vacuum processing system.
2. Background of the Related Art
Vacuum processing systems for processing 150 mm, 200 mm, 300 mm or other size wafers, or substrates, are generally known. A vacuum processing system typically has a centralized transfer chamber mounted on a monolith platform. The transfer chamber is the center of activity for the movement of wafers being processed in the system. Some transfer chambers have multiple facets for mounting chambers of various different types, including process chambers. The process chambers include, among others, rapid thermal processing (RTP) chambers, physical vapor deposition (PVD) chambers, chemical vapor deposition (CVD) chambers, and etch chambers. The process chambers perform various processes on the substrates to form integrated circuits or other structures.
The processes for fabricating IC's or other structures on a substrate, or wafer, typically involve operating in a vacuum environment in a process chamber. Additionally, many of these processes involve generating an ionized plasma discharge in a region of the chamber near the substrate either to strike the substrate with the ions or strike a target to sputter the target material onto the substrate. For example, a physical vapor deposition process typically generates a plasma discharge between a wafer and a target in a very high vacuum. The positive ions in the plasma discharge are accelerated toward the target to dislodge the target material, which then deposits onto the substrate. For example, in order to sputter copper or aluminum onto a wafer, a target fabricated with a copper or aluminum material is mounted in the PVD chamber. A wafer is positioned near the target. A plasma of ions, typically of argon, is struck in the space between the wafer and the target. The ions are accelerated toward the target. The target material is knocked loose from the target and travels onto the surface of the wafer, thereby depositing a thin film of the target material on the wafer. Electrons in the plasma material, along with secondary electrons dislodged from the target material, are attracted to a grounded surface in the chamber, but before these electrons are captured by the grounded surface they typically undergo a sufficient number of ionizing collisions in the plasma to maintain the plasma discharge.
Among other methods, plasma discharges are typically formed in the process chamber by RF voltages, microwaves or planar magnetrons or a combination of techniques. A planar magnetron system, for example, uses a rotating magnetron disposed above a target, and either a dc bias between the target and the substrate or an RF source, coupled into the space between the target and substrate, for powering the discharge to form the plasma. The magnetron is a magnet structure which provides magnetic field lines parallel to, and spaced to the plasma side, of the sputter surface of the target. A negative dc bias voltage between the target and the plasma region accelerates the ions toward the target to dislodge the target material therefrom. The magnetic field from the magnetron confines the free electrons, including the secondary electrons from the target material, near the target to maximize the ionizing collisions by the free electrons with the plasma material before the free electrons are lost to a grounded surface. Where the magnetron is one or more fixed magnets, they typically rotate around the backside, non-sputter side, of the target to evenly spread the magnetic field around the surface of target to result in an even sputtering of the target material.
A simplified example of a PVD chamber 100 is shown in FIG. 1a. Generally, the PVD chamber 100 comprises a substrate support member 102, a target 104 and a magnetron 108. The magnetron is disposed within a cooling chamber 116. The cooling chamber 116 is defined by a top 117, sides 119 and the target 104. A cooling fluid, such as water, flows through the cooling chamber 116.
FIG. 1b shows the magnetron 108. The magnetron 108 has a magnet assembly including several magnets 110. Two stainless steel poles 109, 111 cover the top and the bottom of the magnets 110 to effectively create a more uniform magnetic field across the magnetron 108.
A wafer (not shown) is placed on the substrate support member 102 and raised to a position near the target 104 inside the chamber section 106. The pump section 122, typically a cryopump, pumps the chamber 100 down to a very high vacuum. A motor assembly 112 provides rotational motion to the magnetron 108 through a shaft 114 to rotate the magnetron 108 at about 100 rpm. The plasma is struck in the space between the wafer and the target 104, and ions in the plasma strike the target 104.
The process may heat up the target 104 and the magnetron 108 to about 110.degree. C.-120.degree. C. and about 130.degree. C.-140.degree. C., respectively. If the magnetron 108 and/or the target 104 are heated above the proper temperatures, then the high temperature may alter the performance of the process giving undesirable results and lessening the useful lives of the magnetron 108 and the target 104. At high temperatures, the plasma density and energy may change to alter the sputtering rate or uniformity on the target or the substrate, thereby providing unpredictable results in the process. Additionally, the excessive heat may cause the mechanical features of the magnetron 108 to wear out prematurely. Therefore, water, or other cooling fluid, in the cooling chamber 116 is used to cool the target 104 and the magnetron 108.
The water enters the cooling chamber 116 at an inlet 118, circulates around the magnetron 108 and exits at an outlet 120. The arrows A-F show generalized water flow paths around the magnetron 108. A problem is that the space between the magnetron 108 and the target 104 is only about one millimeter, so very little cooling water can flow therebetween. Thus, it is very difficult to cool this area. Additionally, the rotational motion of the magnetron 108 and frictional engagement of the water therewith creates a centrifugal force to try to push the water away from the rotational center of the magnetron 108 and toward its outer edge. This action of the magnetron 108 causes further difficulties in circulating the water between the magnetron 108 and the target 104. Also, this action of the magnetron 108 combined with the heat generated at the magnetron's rotational center causes water vapor bubbles to form near the rotational center, an effect known as cavitation. These water vapor bubbles cause an abrasive action on the magnets 110 and cause the magnets 110 to wear.
A need, therefore, exists for a process chamber with a mechanism for enhancing the flow of cooling fluid between a rotating member, such as a magnetron in a PVD chamber, and a surface, such as the top side of a sputtering target.